This invention relates to a computer system using virtual memory area, and more particularly to a channel apparatus capable of continuing the data transfer between an input/output device and a main memory even when the block address is changed.
This type of channel apparatus is usually used for the data transfer control between a main memory and a high speed memory device, such as a magnetic disc drive coupled with the channel apparatus. A virtual address used is translated into a real address referring to an address translation table in the main memory. The address translation is generally executed by a microcomputer in the channel device. This translating operation is called a channel DAT (dynamic address translation).
In the conventional channel device, the address translation, writing of the translated real address, or the transfer preparation must be executed by the microcomputer in the channel device every time a block address, for example, a page address is changed. For this reason, the impossibility of data transfer change was a problem every time the page address is changed.
Further, in the conventional channel device, when a channel command word (CCW) with a skip command is executed, a track for restart of the data transfer must be sought in order to execute the next CCW following the execution of the CCW with the skip command. To this end, the microcomputer generates a seek command. However, even though data transfer in response to the seek command is attempted, at the time point of the CCW execution, its intended sector passes over the head of the magnetic disc, and the data cannot be transferred until the disk make one complete rotation. Thus, the problem of reduced throughput was present.